the underlying reason for its development remains obscure; currently the topic of much research

usually an inherited corneal disorder, often in an autosomal recessive fashion

family members may have it, but it also can be random with no other family members affected (sporadic)

most likely that the cause is due to more than one factor

the path that leads to the thinning of the cornea may start with a "trigger", followed by a cascade of events in the eye tissues

the primary trigger is not known.

possible options include hormonal changes in the patient, genetic predisposition to altered cytokines and/or their receptors in the patient's cornea, or a pattern of eye-rubbing that could release factors

abnormal levels of degradative protease activity may then lead to a slow, progressive dissolution of Bowman's layer and the epithelial basement membrane

the epithelium then comes into contact with the stroma, cytokines/growth factors are released, and as a result, the cells begin to produce scar tissue and proteases

a disorder with local micro-environmental changes rather than a situation where the entire cornea is involved

within a single keratoconus cornea there are areas of increased protease activity (thinning) and other areas of ongoing wound healing (scar tissue buildup)

recent advances in molecular techniques make it possible to examine the molecular components in wounded or diseased corneas

CD45 (leukocyte common antigen or T200), a transmembrane phosphotyrosine phosphatase (normally found associated with blood cells), has been found to be present in more cells within keratoconus corneas than normal

these cells may represent the source of some of the proteolytic enzymes reported to be associated with keratoconus

a gene product referred to as glucose regulated protein (GRP78) has been found in greater quantity in normal corneas

a protein that aids or "chaperones" the folding and secretion of other proteins produced in cells

the reduction in GRP78 could affect the secretion and folding of the major structural proteins of the cornea which are reduced in the keratoconus cornea.

some cases have a hereditary component and studies indicate that about 8% of patients have affected relatives

most cases appear to be sporadic

the actual incidence is uncertain, large studies estimate 50 to 230 per 100,000

according to one study, the estimated prevalence in first-degree relatives is 3.34%, which is 15 to 67 times higher than that in the general population (0.23-0.05%). (Am J Med Genet 2000 Aug 28;93(5):403-9 )

early cases may require corneal topography, a test that makes a stereo image which gives a topographic map of the corneal curvature

when advanced, the cornea will be thinner in areas and this can be measured by pachymetry

the biomicroscope is the only tool which allows a clinician to observe many classical signs of keratoconus: Fleischer's ring, stress lines of Vogt, corneal thinning and scarring, various types of staining with and without lens wear, increased visibility of corneal nerves, and corneal hydrops.

in severe cases, a corneal transplant may be needed due to scarring, extreme thinning or contact lens intolerance

a surgical procedure that replaces the keratoconus cornea with healthy donor tissue

20-25% of those with keratoconus ultimately require corneal transplant surgery

success rate of greater than 90%

corneal transplant is warranted when the cornea becomes dangerously thin or when sufficient visual acuity to meet the individual's needs can no longer be achieved by contact lenses due to steepening of the cornea, scaring or lens intolerance

the more severe the keratoconus is, the more likely it is to see a dramatic improvement immediately after surgery

the majority of keratoconus patients have their sutures removed 6-12 months after surgery (depends on healing rate)

a small percentage of transplant patients do obtain uncorrected vision good enough that neither glasses nor contacts are needed after surgery, but in the majority of cases, some form of vision correction is needed after surgery

The National Keratoconus Foundation has a good website with patient resources (www.nkcf.org)

National Keratoconus Foundation

Davis Building, Suite 509

8700 Beverly Boulevard

Los Angeles, CA 90048

(310) 855-6455 Office (800) 521-2524 Hotline (310) 652-8411 Fax

e-mail: nkcf@csmc.edu

The Center for Keratoconus has an excellent website (www.kcenter.org) with links to support groups, patient information, and research studies.

The Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study is a multi-center, observational study, the purpose of which is to characterize vision, corneal changes, and patient quality of life findings in keratoconus and to determine the progression of changes occurring with keratoconus over time. The CLEK Study is an eight-year study. Over 1,200 keratoconus patients are enrolled at 15 participating clinics across the United States. To participate in this study, link to the site through the Digital Journal of Ophthalmology's website (www.djo.harvard.edu).

A keratoconus mailing list is also available for those interested. To subscribe, send "subscribe keratoconus-link YOUR NAME" in the body of a mail message to listproc@ucdavis.edu.